1. Field of the Invention
The present invention generally relates to a bearing assembly and, more particularly, to a wheel support bearing assembly utilizable in automotive vehicles.
2. Description of the Prior Art
It is quite well known that automotive wheels are rotatably supported by suspension systems through respective wheel support bearing assemblies. Those wheel support bearing assemblies are generally required to have a high load carrying capacity and a high rigidity. Also, to increase, for example, the mileage, demands have intensively been made to reduce the weight of component parts used in the automotive vehicles, and the wheel support bearing assembly is not an exception to that.
While most of the conventional wheel support bearing assemblies satisfy the requirement of a high load carrying capacity, it is often considered that the conventional wheel support bearing assemblies would hardly exhibit a sufficient rigidity during cornering of an automotive vehicle. Also, it is recognized that in order to allow the automotive vehicle to travel in a stabilized fashion, the rigidity of the bearing assembly that is exhibited during the cornering must be increased.
The wheel support bearing assemblies are generally employed each in the form of a multi-row bearing and are so designed that during the forward run of the automotive vehicle, the weight of the automotive vehicle may act on an intermediate portion of each multi-row bearing assemblies. However, during the cornering, the moment load tending to incline a hub flange is generated under the influence of the lateral force acting on the respective wheel tire. For this reason, the rigidity of a portion of the multi-row bearing assembly in the region of one of the circular rows of rolling elements such as balls, which is on an outboard side of the bearing assembly, is required to be increased.
The wheel support bearing assembly, in which the rigidity of that portion thereof in the region of one of the circular rows of rolling elements that is on an outboard side of the bearing assembly, has been increased is well suggested in, for example, the Japanese Laid-open Patent Publication No. 2003-232343 and is shown in FIG. 11. Referring to FIG. 11, the wheel support bearing assembly shown therein has two, outboard and inboard, rows Lo and Li of rolling elements 7 and 8 that are shown on left and right sides as viewed therein. Of those rows of the rolling elements, the outboard row Lo includes the rolling elements 7 so arranged as to depict the PCD (pitch circle diameter) greater than that depicted by the inboard row Li of the rolling elements 8. This Japanese patent document also discloses, as an alternative embodiment, the use of the rolling elements 7 of the outboard row Lo, that are greater in number than that of the rolling elements 8 of the inboard row Li, instead of the different PCDs used.
To increase the PCD of the outboard row Lo of the rolling elements 7 to a value greater than that of the inboard row Li of the rolling element or to increase the number of the rolling elements 7 in the outboard row Lo to a value greater than that of the rolling elements 8 in the inboard row Li, such as exemplified by the above mentioned Japanese patent document, brings about an excellent effect of increasing the bearing rigidity in an outboard region of the bearing assembly. Also, since according to the above mentioned Japanese patent document, increase of the pitch circle diameter (PCD) or the number of the rolling elements is effected not in both of the outboard and inboard rows Lo and Li, but only in the outboard row Lo, the overall size and the weight of the bearing assembly do not increase.
However, in the conventional wheel support bearing assemblies, no sufficient consideration has been paid to the shape of the hub axle and, therefore, the effect of increasing the rigidity in the outboard region has not yet been increased satisfactorily. By way of example, in the case of the wheel support bearing assembly shown in FIG. 11, the hub axle 18 that is coupled with the inner race member 19 for rotation together therewith is so configured and so designed that the position Q, at which the inner race member 19 is held in abutment with a shoulder of the inner race mount in the hub axle 18, is at a position on an outboard side of the point intermediate of the ball span as measured between the balls 7 of the outboard row Lo and the balls 8 of the inboard row Li and that an shaft member 18a of the hub axle 18 on an inboard side of the position Q may have an outer diameter equal to that of a reduced diameter portion of the inner race member 19. Because of this unique design, the outer diameter of the shaft member 18a of the hub axle 18 abruptly decreases at a location somewhat on an inboard side of the outboard raceway 5, with the consequence that the rigidity of an outboard end portion of the hub axle 18 is insufficient.
Even on the inboard side, increase of the bearing rigidity is desired in order to facilitate the stabilized run. On the inboard side, it is quite often that the bearing dimensions are limited in the face of their relation with surrounding components and difficulty is often encountered with in increasing the bearing rigidity. In particular, in the case of the wheel support bearing assembly of an inner race rotating type, since an outer member having an inner peripheral surface formed with raceways has to be connected with a knuckle in a fashion engaged with an inner peripheral surface of the knuckle and, therefore, there is no way other than to increase the rigidity with due consideration paid to the limitation brought about by the inner diameter of the knuckle.